The present description refers to a twisting device suitable for simultaneously twisting a plurality of bar electric conductors for making a stator or rotor winding of an electric machine. The present description also refers to an extractor assembly suitable for cooperating with such a twisting device.
It is known to make stators or rotors for electric machines having a stator/rotor core in which a plurality of slots are provided and also comprising a plurality of bar electric conductors inserted into the aforementioned slots and variously interconnected with one another to form one or more stator/rotor windings. The aforementioned stator/rotor windings with bar conductors are commonly called bar stator/rotor windings.
In order to make the aforementioned stator/rotor windings, a twisting device is known to be used, at least in a partially automated manner, suitable for shaping the stator/rotor winding conductors from preformed or bent bar conductors, each having a first and a second arm arranged relatively close to one another or arranged side by side. The known twisting device comprises at least one first body extending around a twisting axis and at least one second body extending around the first body and coaxial with this latter. Such a first and second body are provided with a first and a second circular array of channels, respectively, having centre on the twisting axis. In order to form the winding conductors, a plurality of the aforementioned bar conductors is inserted through a face of the twisting device in the channels provided on the first and on the second body. More in particular, the arms of each bar conductor are inserted into a channel of the first array and in a channel of the second array, respectively. Once the bar conductors have been inserted into the channels, the first and/or the second body are set in rotation around the twisting axis to separate the arms of each bar conductor from one another by an amount equal to a predetermined number of stator or rotor slots.
At the end of such a twisting operation, the winding conductors thus formed are at least partially extracted from the twisting device and finally removed from it through a suitable clamp assembly to subsequently be arranged in the respective slots of the stator or rotor core.
In particular, to extract the winding conductors an extractor assembly is typically used situated directly below the twisting device. Usually, the extractor assembly comprises a first and a second circular array of extraction elements or extraction bars, which are arranged angularly and axially aligned to the channels of the first and of the second body of the twisting device, respectively. Such extraction bars can be moved from the bottom upwards through actuators so that the respective upper end portions can be inserted into the channels of the twisting device so as to lift the winding conductors. A twisting device, an extractor assembly and a clamp assembly of the aforementioned type are described for example in the patent application published as US 2009/0265909.
During the step in which the winding conductors are being extracted from the twisting device, it can occur that some of the extraction bars bend in an undesired manner. This can, for example, be due to an uneven stress on the extraction bars during extraction, which causes in particular a greater axial load on some of such bars. Such an undesired bending of the extraction bars, in an automated process for simultaneously extracting a plurality of winding conductors housed in the channels of the twisting device, can lead to a stop of the production process and to the need to replace or repair the possibly damaged, components, particularly the extraction bars themselves.
It should be observed that such a drawback is experienced more as the length of the extraction bars of the extractor assembly increases. This is particularly important, since there is currently the need to make stator/rotor cores, and consequently also winding conductors, having an increasing axial extension so as to obtain greater performance of the electric machines in which such components are installed. This leads to the need of having twisting devices and extractor assemblies available having channels with increasing depth and extraction bars with increasing length, respectively, which leads to an increase of the possibility of there being the aforementioned drawbacks.
There is thus the need to have a twisting device available suitable for simultaneously twisting a plurality of bar electric conductors, which is, at least partially, able to avoid the aforementioned drawbacks with reference to the prior art.